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convector heater troubles

i have a 2 pipe heat system that uses convectors. i turned the system on yesterday and 2 heaters didnt work. i was able to bleed the air out of one and it is working ok- the other one is not air bound- water came out the bleeder not air, it just isnt getting flow...... the supply line is warm the return line is cold- it is not flowing thru the unit. i noticed that the return line had a valve piped in-line with a flat srew in it for adjustment. i think some debri is blocking the line and not allowing the flow. i loosened the screw which did nothing except start a leak from the screw head. i will need to drain the system to repair the valve blockage. the supply line has a union on the line but the return doesnt- i think i have to saw saw the line at the valve and remove the valve and replace it with a union....... what are the concerns from not having the valve on the return line?

Re: convector heater troubles


This sounds like a classic case of a STATIONARY AIR POCKET somewhere nearby in the supply or return piping that serves the dysfunctional heat convector; I don't think it will do any good to add a union to the air bleed valve or substitute a union for the valve you have on there now---be it on the supply or return side of the convector, this is almost always nevertheless the highest location for that particular convector piping (some exceptions would be if the convector is BELOW the supply piping, as , say in a convector heating a cellar floor area).

Air in most hot water heating pipes will almost always gravitate upward toward the top of a heating pipe system (where the bleed valves can expel it out of the system) because it is lighter than the water, & is being pushed along by the circulator pump; as noted, any entrained air or air bubbles will be carried along by the pump action until it gravitates to a high area of the piping system, which is usually where the air purge valves are located, and the air is easily purged from the system.; there is always entrained air in any NEW WATER that is added to the heating system (perhaps to make up for a small leak, or when service work is done on the piping system---this new water will surrender its air bubbles as the water is heated by the boiler and the bubbles will gravitate toward the upper pipes in the system---that's why it is usually not advisable to add new water to a system, unless service demands require it.

The EXCEPTION to a usually well-functioning piping system occurs when some of the piping for whatever reason begins to slant DOWNWARDS---this could be because the original pipe installer looped the supply/return piping up & over or down and under an I-beam or a large support beam; or perhaps the floor beams in the vicinity of the cold convector have sagged a bit, and the hot water piping that once angled slightly upwards, is now pitched slightly DOWNWARDS---in any event, this creates a pocket where a large air bubble can take up residence, become stationary & shut down the flow of one or two of your convectors.

Google "stationary air pockets" (stationary air pockets in heating pipes) to get a list of sites that treat this problem & offer some things you can try & offers some solutions you can attempt before you request an expensive visit from the heating technician.

One initial, simple attempt that often works for me is to take an ordinary bicycle pump (do not use compressed air under any circumstances), shut off temporarily the water supply valve feeding into the heating system pipes, also temporarily shut off the boiler electrical switch, & place a large plastic cup under the piping & open the bleed valve & hold the business end of the air hose on the bleed valve & give the plunger several strong pumps---then close the bleed valve---you should hear a groaning sound inside the pipes as you force water into the stationary air pocket---you may have to do this several times before the stationary air pocket gets filled with enough water that the pump down at the boiler is able to carry the rest of the entrained air up towards the bleed valve, where it can be removed----when done with the procedure, turn the boiler switch back on & re-open the water supply valve.

You probably will have to do this pipe pumping several times in the coming week before you break up the stationary air bubble & feel good heat coming out of the convector.

Some piping systems have PURGE VALVES located near the boiler---if YOURS does, the boiler can be shut down for 1/2 hour to cool the cast iron/metal system & then a system is set up were a short hose is attached to the purge valve on the RETURN side of the boiler, and dipped in a barrel 1/3 full of water---another supply pipe is attached to the house water supply ( usually at 40-50 psi) and this water is fed to the SUPPLY side of the main piping---when the bubbles stop coming out of the filling barrel of water, it indicates that nearly all the air has been removed from the piping system-----introducing fresh new water into the heating piping also introduces all of the entrained air bubbles that are present in new water, so the system has to be bled regularly after a forced purge---but it often serves to break up any stationary air pockets in the system---this procedure is perhaps best done by a heating technician familiar with hydronic (hot water) heating systems.

At the site below, scroll down & click onto "Contents---Air Removal Filling and Purging"---the book is by Siegenthaler, a big-shot engineer in hydronic heating systems---they want close to $300 bucks for the book!

Hope this helps.


Re: convector heater troubles

thanks- this is an excellent explanation..
there is a bleader valve on the supply line of this heater that has 0 air in it just water- but down on the main supply line the t tap right in front of this line hsa a 2" nipple with a cap on it where a heater was taken off line...... the heater in question used to be the second on line but now is the first on line with 5 following it. my question is- ifit truely was air bound wouldnt all the heaters on this line be effected and not just this one? no work was done to this heater or its pipes prior to this...... the reason for removing the return lines flow valve and adding a union is because when i turned the screw it created a leak at the screw. i dont know if this unit is serviceable or not so i plan to drain the system and look and if not replace with a union.....

Re: convector heater troubles


I always use the air pump method first because it is least invasive & it has a good track record in working for me.

To drain the system & refill, you'll be adding fresh water that always has a lot of entrained air in it; this air will go out of solution once the boiler heats up & you could be back to square one until you bleed the added air out of the system.

Having hard time visualizing your piping arrangement as you describe it; I wonder if you could post a diagram of your piping arrangement, especially as it relates to the non-functioning rad.

Site below demonstrates the different piping schemes used in residential HW systems; also consult again the Siegenthaler
site---these pipes are hidden inside the walls, so it's impossible to see their orientation.


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